reflow profile

The optimal profile to choose is determined by the following factors, (1) thermal mass and distribution across the board, (2) reflow temperature range needed for a particular alloy, (3) the nature of flux. When the thermal mass is small, such as cellular phone, a linear ramp up profile will be the better choice for better wetting, voiding, bridging, wicking, solder beading, and tombstoning. If the thermal mass is large, a conventional soaking zone will be recommended, due to the temperature gradient consideration. For Pb-free soldering, large temperature gradient developed across the board can really damange the board and compromise the reliability. The disadvantage of conventional profile with a soaking zone is a relatively poorer wetting, voiding, bridging, wicking, solder beading, and tombstoning. I have an article on "Optimizing reflow profile via defect mechanisms analysis" discussing the relation between defect mode and profile. You can find it in Proceedings of IPC Printed Circuits Expo �98 or website www.indium.com.

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